Hyperdynamic LV with low stroke volume in septic shock
A 44-year-old man with septic shock is on norepinephrine, MAP 62 mmHg, heart rate 120 bpm, and has received 4 L crystalloid. Bedside echo: LVEF 75%, LVOT diameter 1.8 cm, LVOT VTI 12 cm, no pericardial effusion, mild MR. BSA 1.9 m². The LV cavity appears small and underfilled. The team is considering increasing norepinephrine because the patient remains hypotensive. The ICU asks whether the high ejection fraction means good cardiac output.
1. Calculate stroke volume, cardiac output, cardiac index, and stroke volume index. Interpret the results.
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LVOT CSA = π × (0.9 cm)² = 2.54 cm². SV = 2.54 × 12 cm = 30.5 mL. CO = 30.5 mL × 120 bpm = 3.66 L/min. CI = 3.66/1.9 = 1.93 L/min/m². SVI = 30.5/1.9 = 16.1 mL/m². These are low values: CI below 2.2 L/min/m² and SVI below 35 mL/m². The EF of 75% does not mean good output; EF is stroke volume divided by end-diastolic volume, so a small, underfilled LV can have a high EF with a low SV. This is a low-output state.
2. What physiologic explanations link a high EF to a low stroke volume, and what echo findings would you seek next?
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A high EF with low SV occurs when EDV is reduced (hypovolemia, vasodilation, or impaired filling), when there is dynamic LVOT obstruction, or when stroke volume is lost through MR or a shunt. Sepsis also lowers afterload, which raises EF. Next, measure LV end-diastolic volume and look for SAM and a late-peaking LVOT gradient, assess MR severity, right ventricular function, and IVC filling. A small hyperdynamic LV with a low VTI and no obstruction suggests underfilling and vasodilation; if SAM appears, fluids or inotropes may worsen obstruction. Repeat after a passive leg raise or fluid challenge to assess responsiveness.
3. How would you use these data to guide therapy? What are the limitations of the LVOT VTI method?
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The data argue against simply increasing norepinephrine as the only response; low SVI/CI suggests the patient may need additional volume or inotropic support, but this depends on whether dynamic LVOT obstruction or fluid responsiveness is present. Use dynamic assessments such as passive leg raise and changes in LVOT VTI, and repeat echo after each intervention. Limitations of the LVOT VTI method: it assumes a circular, constant LVOT and a uniform velocity profile; the diameter is squared, so small errors matter; angle and sample-volume errors affect VTI; arrhythmia and MR reduce reliability; and with SAM the measured VTI may reflect obstruction rather than forward output. If uncertainty is high, use an independent method such as thermodilution or 3D echo.